Method and apparatus for heat treatment of glass material and natural materials specifically of volcanic origin

ABSTRACT

A method of heat treatment of glass materials and natural materials specifically of volcanic origin according to which the treated material is exposed to microwave radiation at a frequency range from 1 MHz to 10 GHz and temperature range from the ambient temperature to 1800° C. in a batch or continuous process. The glass or natural material subjected to a melting and/or refining process contains an inert additive elected from the group comprising carbides, nitrides or borides in an amount from 1 to 100 g preferably 5 to 50 g per 1 kg of the glass or natural material. The apparatus consists substantially of a microwave furnace comprising an outer shell ( 8.2 ) provided with a cover ( 10 ) and an inner shell ( 8.1 ) and at least one micro wave generator ( 1.1, 1.2, 1.3, 1.4 ) with double emission and total power from 0.1 to 1 kW per 1 kg of the treated material.

CROSS REFERENCE TO RELATED APPLICATIONS

Applicant claims priority under 35 U.S.C. §119 of Czech RepublicApplication Nos. PV 1999-2185, PV 2000-968, and PV 2000-1935 filed Jun.17, 1999, Mar. 17, 2000, and May 25, 2000, respectively. Applicant alsoclaims priority under 35 U.S.C. 365 of PCT/CZ00/00042 filed Jun. 12,2000. The international application under PCT article 21(2) waspublished in English.

FIELD OF INVENTION

The invention relates to a method of heat treatment glass and naturalmaterials specifically of volcanic origin. Under the heat treatment ofglass materials it is to be understood melting or refining of glasscullet, glass batches or mixtures thereof or hardening or forming glass.The materials of volcanic origin such as basalt, granite, marble,andesite, syenite, etc. are accordingly subjected to melting or refiningor hardening and forming to obtain utility goods such as floor tiles,wall tiles, rods, bars, fibers, insulating wool, artistic objects andvarious glassware etc. In addition, the invention relates to anapparatus for performing this method.

DESCRIPTION OF PRIOR ART

At the present time the melting of glass or production of glass melt ormother glass as well as melting of natural materials specifically ofvolcanic origin such as basalt is effected almost exclusively inglassmaking furnaces or melting furnaces heated by gas burners. Suchfurnaces show heavy weight and robustness. The furnace is to be heatedas a whole and must be provided with thick insulation layers—fireclaywhat considerably affects its mobility i.e. the possibility of moving itfrom place to place for example for exhibition purposes. Moreover, thecombustion of considerable amount of gas results in the generation ofnotably amount of hazardous flue gases affecting environment and also instrong heat radiation into the working place area what makes the workingconditions unpleasant. There have been efforts to replace suchglassmaking furnaces by electrically heated furnaces but due to specificparameter requirements such as temperature, glass output and energyconsumption such efforts resulted in their limited use mostly foreconomic reasons. The requirement for quick melting of glass or naturalmaterials by classic heating methods faces the main problem ofconsiderably low thermal conductivity of such materials. In addition,certain types of glasses or materials especially those containing ironsuch as welding glass or basalt effectively reflect the infraredradiation so the temperature profile is sharply decreasing from thesurface to the inside of the material so that the thickness of the batchmaterial must be limited.

Attempts to make use of a micro wave technology has encountered seriousdifficulties since most types of glass are well transparent for microwave i.e. glass does not absorb microwaves at the ambient temperatureand has to be activated in some way i.e. make it capable to absorbmicrowaves. It is also known that at certain temperature—about 500° C.and more the positively charged particles of alkaline ions vibrating inthe negative charged interstitial position begins to act as oscillatingdipole which is the basic condition for absorption of microwaves. Thepre-heating may be effected for example by electrical heating what ofcourse requires a hybrid furnace i.e. a furnace provided with combinedelectric and microwave heating which design is relatively costly andrestrictive in capacity. Some authors have used for the preheating oftransparent materials such as asbestos and kieselguhr various additivescapable to absorb microwaves, for example powdered iron, irontrichloride, or borax (F. G. Wihsmann, R. Kokoschko, K. Forkel,“Glassmaker and Ceramicmaker” 46 75 (1996). However, such materialsproved to be unsuitable as additives to glass materials since they reactwith the glass mass and undesirably change the glass composition andstructure. Other authors used for the batch preheating a microwaveabsorbing envelop or they hydrated the material before its melting (M.P. Knox, GI. J. Copley, “Glass technology” 38, 91 (1997). Neither theseactivating methods are perfect since by using a wave absorbing envelopthe microwaves are hindered from penetrating into the batch and theheating is distributed by radiation as in the case of the classicheating processes. On the other hand with the majority of types of glassneither the hydration nor wetting provides sufficient means to warm upthe batch to the temperature required.

According to EP-A1-0 349 405 micro waves are used for preheating orheating of materials such as oxides, glass and certain metals producingcorrosive effect on the furnace lining when subjected to an inductionheating. To enable preheating of materials that are not susceptible tomicro waves glass containing iron oxides is added to the batch whichoxide due to its high micro wave absorption provides for heating of theremaining micro-waves not susceptible materials. Nevertheless, suchprocess is unacceptable for production of most of types of glass ornatural materials based products since the iron oxide substantiallyaffect the required qualities of final products.

The object of the invention is to provide a new method of heat treatmentof glass materials and natural materials specifically of volcanic originwhich enables melting, refining or hardening of such materials underspecific conditions by applying the microwave technology in the fulltemperature range required and to all types of materials notwithstandingthe composition or structure thereof.

Another object of the invention is to provide an apparatus forperforming said method operated in both the batch or continuous process.

SUMMARY OF THE INVENTION

In accordance with the foregoing the treated material is exposed tomicrowave radiation at frequency range from 1 MHz to 10 GHz andtemperature range from the ambient temperature to 1800° C. in a batch orcontinuous production process.

More specifically, the frequency of the microwave radiation is electedwithin the range from 1 to 100 MHz, preferably 27 MHz, from 500 MHz to10 GHz preferably 896 MHz, 915 MHz and 2450 MHz.

To ensure safe and quick heating throughout the full temperature rangethe glass or natural material that is subjected to a melting and/orrefining process contains an inert additive selected from the groupcomprising carbides, nitrides or borides in an amount from 1 to 100 gpreferably 5 to 50 g per 1 kg of the glass or natural material.

More specifically, the inert additive is elected from the groupconsisting of tungsten carbide—WC, silicon carbide—SiC, boroncarbide—B₄C, titanium carbide—TiC or vanadium nitride—VN, boronnitride—BN, silicon nitride—Si₃N₄ or titanium boride—TiB₂, niobiumboride—NB₂, vanadium boride—VB₂, tungsten boride —WB₂, zirkonium borideZrB₂, and aluminum boride AIB₂ or a mixture thereof.

The glass material may comprise glass cullet form common waste glass ofany kind or glass batches of all types or mixtures of glass cullet andglass batch and the natural material may comprise basalt, granite,marble, andesite, syenite, and other materials absorbing the micro waveradiation.

An apparatus for performing the method consists substantially of amicrowave furnace comprising an outer shell provided with a cover and aninner shell and at least one microwave generator with double emissionand total power from 0.1 to 1 kW per 1 kg of the processed glass ornatural material arranged substantially in the intermediate space inbetween the outer shell and inner shell and a tank disposed inside theinner shell.

The inner space of the furnace is advantageously filled up with a heatinsulating material having a heat resistance up to 1750° C. elected fromthe group consisting of aluminum oxide—corrandum and siliconoxide—quartz and the furnace cover is provided with at least one safetyswitch and a fill neck engaging a contactless infrared sensor with aconnection for transmitting its signal to a thermometer and controllerprovided with a microprocessor for the microwave generator control. Toenable continuous process the tank is provided with a side or bottomtapping point. The easy mobility of the furnace is secured bytransporting wheels mounted on the outer shell.

The method and apparatus according to the invention are based on theapplication of microwave energy for selective heating of glass, glassmaterials, natural materials especially of volcanic origin such asbasalt, granite, marble etc. The applied technology may ensure that onlythe material required to be heated up is exposed to the heating effectuniformly in its whole volume while the adjacent space remainsunaffected by the heat. In this way the supplied energy is usedexclusively for melting, refining or hardening of the material requiredand it is not necessary to heat up the whole body of the furnace.

Another advantage of the invention results from applying inert materials(for example silicone carbide) as additives to the glass mass or batch.Such inert materials are strong absorbers of microwaves even at theambient temperature while the properties of glass or natural materialsremain unaffected. In this way any type of glass may be meltednotwithstanding the extent to which the glass is capable to absorbmicrowaves as well as the glass composition and particles size includingany glass batches or natural materials specifically of volcanic origincontaining a metal for example. The melting process is extremelyaccelerated and is determined only by the heat resistance of a ceramiccrucible. A metallic or graphite crucible cannot be used due to theirunfavorable interaction with microwaves.

Any undesirable phenomena such as material loss or its oxidation by airoxygen are fully suppressed in the microwave melting process. Therequired properties of the material processed are completely preservedyet may be altered by a controlled modification of the melting regime.For example, by an appropriate application of the microwave energy in aglass batch melting process glass of different properties may beobtained that cannot be produced in the classic glassmaking furnaces(for example with respect to its morphology, microstructure ormechanical strength etc.).

The advantages of the invention based on the application of microwaveheating technology including modified microwave furnace may besummarized as follows:

-   -   quick and in volume heating—the in volume heating means the        effect of microwaves to heat materials almost uniformly from the        volume center to its outer border in contrast to the classic        heating;    -   selective heating—the selective heating means that only the        material required is heated up while its surrounding remains        cool;    -   the furnace need not be permanently supplied by energy—the        furnace may be switched on or off at any time, i.e. it need not        be operated continuously;    -   low electric energy consumption resulting in substantially lower        operation costs—this benefit arises from the preceding        attributes;    -   harmless working conditions—no hazardous combustion gases are        generated neither the temperature at the working place is        increased.

In addition, besides for the mere melting purposes the furnace may beused for refining, hardening or forming of various glass materials,melting of several glass samples for example to serve the purpose ofcolor decorations or processing of molten natural materials to produceutility goods such as floor tiles, wall tiles, rods, bars, fibersinsulating wool artistic objects etc.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawing shows a schematic vertical sectional view ofone possible embodiment of the apparatus according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT EXAMPLE 1

5 kg of crushed transparent glass cullet of particle size from 2 to 6 mmand 100 g of compact tungsten carbide (WC) were charged into a ceramiccrucible with a capacity of 4 liters (l) in volume whereupon thecrucible was put into a microwave furnace. After closing the furnacecover the crucible contents was heated up by means of microwaveradiation with a frequency 2450 MHz and power 4 kW until the batch wasmelt. The glass melt was maintained at a temperature of 1200±50° C. andprocessed in forming various utility items.

EXAMPLE 2

2 kg of the mixture consisting of a lead crystal batch and 50 g ofcompact tungsten carbide (WC) were charged into a ceramic crucible withthe capacity of 4 liters then the crucible was put into a microwavefurnace. After closing the furnace cover the crucible contents washeated by microwave radiation at a frequency of 2450 MHz and power 2 kWuntil the glass was melted and then the glass melt was refined at atemperature of 1450° C. and thereafter at 1200±20° C. The glass melt wasfurther maintained at this temperature and utilized in production ofvarious utility items.

EXAMPLE 3

The glassmaking process according to example 2 was repeated undersubstantially the same conditions with the exception that as additivesthe following compounds were employed one after other: tungstencarbide—WC, silicon carbide —SiC, boron carbide—B₄C, titaniumcarbide—TiC or vanadium nitride—VN, boron nitride—BN, siliconnitride—Si₃N₄ or titanium boride—TiB₂, niobium boride—NB₂, vanadiumboride—VB₂, tungsten boride—WB₂, zirkonium boride ZrB₂, and aluminumboride AIB₂.

EXAMPLE 4

10 kg of glass cullet originating from the waste packing glass such asbottles, jars etc. and 200 g of the compact tungsten carbide (WC) wereplaced inter a ceramic tank 10 liters by volume provided with a side orbottom tapping point. The tank was placed into a microwave furnace whichwas closed and switched on to run at the highest power. The glass culletwas melted and refined by the micro wave radiation effect and the glassmelt was withdrawn through the bottom or a side tapping point to befurther processed. The furnace was provided with inlet and outlet meansso that the whole process could be carried out in a continuos mode.

EXAMPLE 5

5 kg of glass crushed basalt of particle size from 0.2 to 60 mm were putinto a ceramic crucible with the capacity of 4 liters and the cruciblewas placed into a microwave furnace. After closing the furnace the batchin crucible was heated by a micro wave radiation at a frequency of 2450MHz and power 4 kW until the batch was completely melted at atemperature of 1600° C. and then this temperature was reduced to 1200°C. The molten basalt was then maintained at 1200±20° C. and furtherprocessed in various utility goods.

EXAMPLE 6

8 kg of crushed basalt of particle size from 0.2 to 60 mm were put intoa ceramic crucible having the capacity of 10 liters and the crucible wasput into a microwave furnace. After closing the furnace the batch in thecrucible was heated by microwave radiation at a frequency of 915 MHzuntil the batch was completely molten at a temperature 1400° C. and thenthis temperature was decreased to 1200° C. The molten basalt was thenmaintained at a temperature of 1200° C. and further formed by drawing tofibers or blowing to an insulating wool.

EXAMPLE 7

30 kg of natural material selected from the group consisting of basalt,granite, marble, optionally in mixture with additives selected from thegroup of carbides, nitrides and borides in an amount of 1 to 10% byweight for the purpose of accelerating of the melting were put into aceramic tank with the capacity of 20 liters. The material was melted bythe effect of microwave energy and maintained molten at a temperaturefrom 1400 to 1450° C. and then withdrawn through a bottom outlet.Simultaneously, the amount of the withdrawn molten material wascompensated by substantially continuous supply of a raw material whereinthe feed rate was controlled in order to maintain a substantiallyconstant volume of the molten material in the tank.

EXAMPLE 8

A batch or alternatively continuous operated glassmaking furnacecomprises an outer shell 8.2 and an inner shell 8.1. The inner shell 8.1defines a heat insulated inner space which is filled up with aninsulating refractory material 3 of aluminum oxide—corundum. Thismaterial is permeable for microwaves even at high temperatures.Microwave generators called magnetrons 1.1, 1.2, 1.3, 1.4 are mounted onthe inner shell 8.1 and extend into the intermediate space between theinner shell 8.1 and the outer shell 8.2. In this intermediate space fans4 for cooling magnetrons 1.1-1.4, are located. The upper part of theglass furnace is provided with a cover 10 having an upwardly projectingfill neck 7. The fill neck 7 is connected over a conduit 12 to a storagereservoir 11 of batch material. The cover 10 is further provided by twosafety switches 9.1, 9.2. The fill neck 7 is engaged with an infraredsensor 5 connected to a thermometer and temperature controller 6equipped with a microprocessor for controlling the operation of thefurnace. The bottom of the outer shell 8.2 is fitted with transportwheels 14. A tank 2 for receiving the batch material is situated in theinsulated space its upper part being connected to the fill neck 7 whilethe bottom thereof is connected to the tapping point 13.

At least four micro waves generators—magnetrons 1.1–1.4 are installed togenerate microwaves energy at a frequency of 2450 MHz with single ordouble emission in order to provide as much as possible homogenouselectromagnetic field. The total microwave power may be adjusted withrespect to the quantity of the natural material batch within the rangefrom 2 to 6 kW, preferably 4 kW per 10 to 15 kg of the batch. Thetemperature of the molten material is measured by a contactless infraredsensor 5 and regulated by a thermometer coupled to a controller 6equipped with a process controlling microprocessor. The mechanicalsafety switches 9.1 and 9.2 provided on the cover 10 prevent themicrowave radiation from scattering into the furnace surroundings whenthe furnace is opened so that they switch off the energy supply to themagnetrons 1.1–1.4.

In operation, the batch material is supplied continuously orsemi-continuously from the storage reservoir 11 to the tank 2 throughthe fill neck 12 where the batch material is melted and refined andsubsequently withdrawn continuously or semi-continuously through thetapping point 13.

INDUSTRIAL APPLICABILITY

The invention may be used for melting or production of all types ofglass and natural materials especially of volcanic originnotwithstanding the extent to which such materials are capable to absorbmicrowaves. The processes under invention in combination with amicrowave furnace may be used in glass factories for laboratory purposes(for example for the preparation of common, modified or new types ofglasses) for artistic purposes (production of artistic objects, replicasetc.) for decorative purposes (decoration of basic shapes with variouskinds of colored glass).

In summary, the invention may be used in glass factories, laboratories,studious, artistic studious, home glass shops and similar works and insimilar facilities for melting and processing basalt and like materialsto produce insulating wool, fibers or utility items such as floor andwall tiles including without limitation vases, bowls and statues. Thanksto the easy mobility of the microwave furnace the inventive process andfurnace may be used at exhibitions and fairs for demonstration of theproduction glassware and other goods of natural materials as a part ofmanufacturers promotion of their products as well as for teaching andtraining purposes at professional schools of applied and decorativearts.

1. A method of heat treatment of glass materials and natural materials of volcanic origin selected from the group consisting of basalt, granite, marble, andesite, and syenite, the method including melting and refining said glass and natural materials to form objects, comprising exposing the glass and natural materials to microwave radiation at a frequency range from 1 MHz to 10 GHz and at a temperature range from the ambient temperature to 1800° C. in a batch or continuous production process in a presence of an inert, microwave absorbing additive selected from the group consisting of carbides, nitrides, or borides in an amount from 1 to 100 g per 1 kg of the glass materials or natural materials.
 2. The method of heat treatment of glass materials and natural materials of claim 1, wherein the frequency of microwave radiation is in a range selected from the group consisting of 1 to 100 MHz and 500 MHz to 10 GHz.
 3. The method of heat treatment of glass materials and natural materials of claim 1, wherein the frequency of microwave radiation is selected from the group consisting of 27 MHz, 896 MHz, 915 MHz and 2450 MHz and the amount of the inert additive is from 5 to 50 g per 1 kg of the glass materials or natural materials.
 4. The method of heat treatment of glass materials and natural materials of claim 3, wherein the inert additive is selected from the group consisting of tungsten carbide—WC, silicon carbide—SiC, boron carbide—B₄C, titanium carbide—TiC or vanadium nitride—VN, boron nitride—BN, silicon nitride—Si₃N₄ or titanium boride—TiB₂, niobium boride—NB₂, vanadium boride—VB₂, tungsten boride—WB₂, zirconium boride ZrB₂, and aluminum boride AlB₂ and a mixture thereof.
 5. The method of heat treatment of glass materials and natural materials of claim 1, wherein the glass materials comprise cullet of common waste glass of any kind or glass batches of all types of mixtures of cullet and glass and glass batches.
 6. An apparatus for heat treatment of glass materials and natural materials, comprising a microwave furnace comprising: an outer shell provided with a cover and an inner shell and at least one microwave generator with double emission and a total output from 0.1 to 1 kW per 1 kg of the processed glass materials or natural materials arranged substantially in an intermediate space between the outer shell and the inner shell; and an insulating, material having a heat resistance up to 1750° C. and being selected from the group consisting of aluminum oxide—corundum and silicon oxide—quartz.
 7. The apparatus of claim 6, wherein the tank is provided with a fill-neck and a side or bottom tapping point. 